The present invention relates to a color image forming device having an intermediate image transfer member and a plurality of electrostatic latent image bearing bodies disposed following the movement direction of the intermediate image transfer member. Each of the electrostatic latent image bearing bodies is for developing a different color of an image.
A tandem type color image forming device has been known in which toners of cyan, magenta, yellow and black are contained in respective developing units, and electrostatic latent image bearing bodies each disposed beside each developing unit are aligned in a direction. According to the tandem type device, developing operations in the respective developing units are performed almost concurrently. Therefore, color image can be formed at high speed.
However, in the conventional tandem type color image forming device, a plurality of process units each including a photosensitive drum and a developing device are arrayed linearly in a direction parallel with an installing floor for the image forming device. Consequently, large installation area is required.
To avoid this problem, Japanese Patent Application publication No. Hei-8-190245 discloses a color image forming device in which the plurality of the process units are arrayed in a vertical direction to reduce the installation area of the entire device. However, in the disclosed color image forming device, a sheet discharge tray projects from a side wall of the image forming device, and each developing device is bulky and has a complicated construction. Consequently, resultant image forming device becomes bulky.
Further, in the conventional device, a vertical side wall plate is pivotably supported to a main frame, so that the side wall plate can be opened and closed for exchanging the process unit with a new unit. The vertical side wall plate extends in a direction perpendicular to each rotation axis of each photosensitive drum. That is, the side wall plate is positioned in confrontation with each end of each photosensitive drum. At this place, there is provided a mechanism for positioning the rotation shaft of the photosensitive drum, or a mechanism for positioning a rotation shaft of a drive roller for driving the intermediate image transfer belt. These mechanisms will become obstacles against the exchanging work, and will degrade the accurate positioning of the exchanged process unit. As a result, color image displacement may occur in the resultant color image in which one color image is slightly displaced from the other color images.